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| <p><strong>Bombardment History of the Inner Solar System</strong></p> |
| <p>Renu Malhotra</p> |
| <p><em>Department of Planetary Sciences</em></p> |
| <p><em>University of Arizona</em></p> |
| <p><em>1629 East University Boulevard, Tucson AZ 85721-0092</em></p> |
| <p><em>USA</em></p> |
| <p>renu@lpl.arizona.edu</p> |
| <p>Robert G. Strom</p> |
| <p><em>Department of Planetary Sciences</em></p> |
| <p><em>University of Arizona</em></p> |
| <p><em>1629 East University Boulevard, Tucson AZ 85721-0092</em></p> |
| <p><em>USA</em></p> |
| <p>Takashi Ito</p> |
| <p><em>National Astronomical Observatory</em></p> |
| <p><em>Osawa, Mitaka, Tokyo 181-8588</em></p> |
| <p><em>JAPAN</em></p> |
| <p>Fumi Yoshida</p> |
| <p><em>National Astronomical Observatory</em></p> |
| <p><em>Osawa, Mitaka, Tokyo 181-8588</em></p> |
| <p><em>JAPAN</em></p> |
| <p>David A. Kring</p> |
| <p><em>Department of Planetary Sciences</em></p> |
| <p><em>University of Arizona</em></p> |
| <p><em>1629 East University Boulevard, Tucson AZ 85721-0092</em></p> |
| <p><em>USA</em></p> |
| <p>We show that the impact crater record of the terrestrial planets and the Moon is owed to two populations of impactors that are distinguishable by their size distributions. We further show that the ‘old' population, responsible for an intense period of bombardment that ended 3.8 Gigayears ago, is virtually identical in size distribution to the present main belt asteroids; the second population, responsible for craters younger than 3.8 Gy, matches closely the size distribution of the near earth asteroids. These results confirm that an inner Solar System impact cataclysm occurred 3.9 Gy ago, and also provide compelling new evidence that identifies the main asteroid belt as the source of the impactors. Comets cannot have been a significant impactor source for the crater record.</p> |
| <p>A plausible explanation is that many asteroids were ejected from the main belt on a short timescale, ~107 y, by sweeping gravitational resonances during an epoch of orbital migration of the giant planets in early Solar System history. The impactors in the inner Solar System over the past 3.8 Gy are also derived from the asteroid belt, but by a combination of chaotic gravitational resonances and non-gravitational processes; the latter process being size-dependent, yields a size distribution quite distinct from the purely gravitational process that caused the cataclysm 3.9 Gy ago. Several important implications for the evolution of asteroids, for planetary geology, and for the origin and history of the Solar System follow from these results. [Reference: Strom et al., Science 309:1847-1850 (2005).]</p> |
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